Measuring the Deliquescence Point of Crystalline Sucrose as a Function of Temperature Using a New Automatic Isotherm Generator

Abstract

The relative humidity at which crystalline materials begin adsorbing large quantities of water from the atmosphere, termed the deliquescence point (RH_o), is an important temperature dependent stability parameter. The RH_o of a number of food and pharmaceutical materials has been determined at 25°C, but it is difficult to find RH_o values in the literature at other temperatures, even for common food materials, such as sucrose. Thus, the primary objective of this research was to assess the effect of temperature on RH_o for crystalline sucrose using a new automatic isotherm generator. A secondary objective was to determine and compare the RH_o value using three other methods (RH after the MC step change method, and two smoothing and second derivative methods [Savitzky-Golay and Yuan and others]), in addition to the commonly used linear extrapolation method. The AquaSorp DDI method provides an accurate, fast, and convenient means of measuring the initial real-time a_w values of the adsorption of water by the crystalline solid, making the DDI method an outstanding RH_o measuring method. A decrease in RH_o with increasing temperature was observed and attributed to increasing sucrose solubility with increasing temperature. No statistical difference (p = 0.05) was found between the four RH_o determination methods at each temperature, with the linear extrapolation method yielding RH_o values of 85.9, 85.7, and 84.0% at 15, 25, and 35°C, respectively.

Keywords:

• Sucrose
• Deliquescence
• Water activity
• Relative humidity
• AquaSorp isotherm generator

ACKNOWLEDGMENTS

The authors would like to acknowledge the support of Kraft Foods for their contribution to the joint Undergraduate and Masters Program between the University of Illinois, Urbana-Champaign, IL and China Agricultural University, Beijing, China. The use of the AquaSorp instrument from Decagon Devices Inc. (Pullman, WA) is also gratefully acknowledged.

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